NAME

zshmisc - everything and then some

SIMPLECOMMANDS&PIPELINES

A simplecommand is a sequence of optional parameter assignments
followed by blank-separated words, with optional redirections
interspersed. The first word is the command to be executed, and the
remaining words, if any, are arguments to the command. If a command
name is given, the parameter assignments modify the environment of the
command when it is executed. The value of a simple command is its exit
status, or 128 plus the signal number if terminated by a signal. For
example,
echofoo
is a simple command with arguments.
A pipeline is either a simple command, or a sequence of two or more
simple commands where each command is separated from the next by `|' or
`|&'. Where commands are separated by `|', the standard output of the
first command is connected to the standard input of the next. `|&' is
shorthand for `2>&1|', which connects both the standard output and the
standard error of the command to the standard input of the next. The
value of a pipeline is the value of the last command, unless the
pipeline is preceded by `!' in which case the value is the logical
inverse of the value of the last command. For example,
echofoo|sed's/foo/bar/'
is a pipeline, where the output (`foo' plus a newline) of the first
command will be passed to the input of the second.
If a pipeline is preceded by `coproc', it is executed as a coprocess; a
two-way pipe is established between it and the parent shell. The shell
can read from or write to the coprocess by means of the `>&p' and `<&p'
redirection operators or with `print-p' and `read-p'. A pipeline
cannot be preceded by both `coproc' and `!'. If job control is active,
the coprocess can be treated in other than input and output as an
ordinary background job.
A sublist is either a single pipeline, or a sequence of two or more
pipelines separated by `&&' or `||'. If two pipelines are separated by
`&&', the second pipeline is executed only if the first succeeds
(returns a zero status). If two pipelines are separated by `||', the
second is executed only if the first fails (returns a nonzero status).
Both operators have equal precedence and are left associative. The
value of the sublist is the value of the last pipeline executed. For
example,
dmesg|greppanic&&printyes
is a sublist consisting of two pipelines, the second just a simple
command which will be executed if and only if the grep command returns
a zero status. If it does not, the value of the sublist is that return
status, else it is the status returned by the print (almost certainly
zero).
A list is a sequence of zero or more sublists, in which each sublist is
terminated by `;', `&', `&|', `&!', or a newline. This terminator may
optionally be omitted from the last sublist in the list when the list
appears as a complex command inside `(...)' or `{...}'. When a sublist
is terminated by `;' or newline, the shell waits for it to finish
before executing the next sublist. If a sublist is terminated by a
`&', `&|', or `&!', the shell executes the last pipeline in it in the
background, and does not wait for it to finish (note the difference
from other shells which execute the whole sublist in the background).
A backgrounded pipeline returns a status of zero.
More generally, a list can be seen as a set of any shell commands
whatsoever, including the complex commands below; this is implied
wherever the word `list' appears in later descriptions. For example,
the commands in a shell function form a special sort of list.

PRECOMMANDMODIFIERS

A simple command may be preceded by a precommandmodifier, which will
alter how the command is interpreted. These modifiers are shell
builtin commands with the exception of nocorrect which is a reserved
word.
- The command is executed with a `-' prepended to its argv[0]
string.
builtin
The command word is taken to be the name of a builtin command,
rather than a shell function or external command.
command [ -pvV ]
The command word is taken to be the name of an external command,
rather than a shell function or builtin. If the POSIX_BUILTINS
option is set, builtins will also be executed but certain
special properties of them are suppressed. The -p flag causes a
default path to be searched instead of that in $path. With the
-v flag, command is similar to whence and with -V, it is
equivalent to whence-v.
exec [ -cl ] [ -aargv0 ]
The following command together with any arguments is run in
place of the current process, rather than as a sub-process. The
shell does not fork and is replaced. The shell does not invoke
TRAPEXIT, nor does it source zlogout files. The options are
provided for compatibility with other shells.
The -c option clears the environment.
The -l option is equivalent to the - precommand modifier, to
treat the replacement command as a login shell; the command is
executed with a - prepended to its argv[0] string. This flag
has no effect if used together with the -a option.
The -a option is used to specify explicitly the argv[0] string
(the name of the command as seen by the process itself) to be
used by the replacement command and is directly equivalent to
setting a value for the ARGV0 environment variable.
nocorrect
Spelling correction is not done on any of the words. This must
appear before any other precommand modifier, as it is
interpreted immediately, before any parsing is done. It has no
effect in non-interactive shells.
noglob Filename generation (globbing) is not performed on any of the
words.

COMPLEXCOMMANDS

A complexcommand in zsh is one of the following:
iflistthenlist [ eliflistthenlist ] ... [ elselist ] fi
The iflist is executed, and if it returns a zero exit status,
the thenlist is executed. Otherwise, the eliflist is executed
and if its status is zero, the thenlist is executed. If each
eliflist returns nonzero status, the elselist is executed.
forname ... [ inword ... ] termdolistdone
where term is at least one newline or ;. Expand the list of
words, and set the parameter name to each of them in turn,
executing list each time. If the inword is omitted, use the
positional parameters instead of the words.
More than one parameter name can appear before the list of
words. If Nnames are given, then on each execution of the loop
the next Nwords are assigned to the corresponding parameters.
If there are more names than remaining words, the remaining
parameters are each set to the empty string. Execution of the
loop ends when there is no remaining word to assign to the first
name. It is only possible for in to appear as the first name in
the list, else it will be treated as marking the end of the
list.
for(( [expr1] ; [expr2] ; [expr3] ))dolistdone
The arithmetic expression expr1 is evaluated first (see the
section `Arithmetic Evaluation'). The arithmetic expression
expr2 is repeatedly evaluated until it evaluates to zero and
when non-zero, list is executed and the arithmetic expression
expr3 evaluated. If any expression is omitted, then it behaves
as if it evaluated to 1.
whilelistdolistdone
Execute the dolist as long as the whilelist returns a zero
exit status.
untillistdolistdone
Execute the dolist as long as untillist returns a nonzero exit
status.
repeatworddolistdoneword is expanded and treated as an arithmetic expression, which
must evaluate to a number n. list is then executed n times.
The repeat syntax is disabled by default when the shell starts
in a mode emulating another shell. It can be enabled with the
command `enable-rrepeat'
casewordin [ [(] pattern [ |pattern ] ... )list (;;|;&|;|) ] ...
esac
Execute the list associated with the first pattern that matches
word, if any. The form of the patterns is the same as that used
for filename generation. See the section `Filename Generation'.
If the list that is executed is terminated with ;& rather than
;;, the following list is also executed. The rule for the
terminator of the following list ;;, ;& or ;| is applied unless
the esac is reached.
If the list that is executed is terminated with ;| the shell
continues to scan the patterns looking for the next match,
executing the corresponding list, and applying the rule for the
corresponding terminator ;;, ;& or ;|. Note that word is not
re-expanded; all applicable patterns are tested with the same
word.
selectname [ inword ... term ] dolistdone
where term is one or more newline or ; to terminate the words.
Print the set of words, each preceded by a number. If the inword is omitted, use the positional parameters. The PROMPT3
prompt is printed and a line is read from the line editor if the
shell is interactive and that is active, or else standard input.
If this line consists of the number of one of the listed words,
then the parameter name is set to the word corresponding to this
number. If this line is empty, the selection list is printed
again. Otherwise, the value of the parameter name is set to
null. The contents of the line read from standard input is
saved in the parameter REPLY. list is executed for each
selection until a break or end-of-file is encountered.
(list)
Execute list in a subshell. Traps set by the trap builtin are
reset to their default values while executing list.
{list}
Execute list.
{try-list}always{always-list}
First execute try-list. Regardless of errors, or break,
continue, or return commands encountered within try-list,
execute always-list. Execution then continues from the result
of the execution of try-list; in other words, any error, or
break, continue, or return command is treated in the normal way,
as if always-list were not present. The two chunks of code are
referred to as the `try block' and the `always block'.
Optional newlines or semicolons may appear after the always;
note, however, that they may not appear between the preceding
closing brace and the always.
An `error' in this context is a condition such as a syntax error
which causes the shell to abort execution of the current
function, script, or list. Syntax errors encountered while the
shell is parsing the code do not cause the always-list to be
executed. For example, an erroneously constructed if block in
try-list would cause the shell to abort during parsing, so that
always-list would not be executed, while an erroneous
substitution such as ${*foo*} would cause a run-time error,
after which always-list would be executed.
An error condition can be tested and reset with the special
integer variable TRY_BLOCK_ERROR. Outside an always-list the
value is irrelevant, but it is initialised to -1. Inside
always-list, the value is 1 if an error occurred in the
try-list, else 0. If TRY_BLOCK_ERROR is set to 0 during the
always-list, the error condition caused by the try-list is
reset, and shell execution continues normally after the end of
always-list. Altering the value during the try-list is not
useful (unless this forms part of an enclosing always block).
Regardless of TRY_BLOCK_ERROR, after the end of always-list the
normal shell status $? is the value returned from always-list.
This will be non-zero if there was an error, even if
TRY_BLOCK_ERROR was set to zero.
The following executes the given code, ignoring any errors it
causes. This is an alternative to the usual convention of
protecting code by executing it in a subshell.
{#codewhichmaycauseanerror}always{#Thiscodeisexecutedregardlessoftheerror.((TRY_BLOCK_ERROR=0))}#Theerrorconditionhasbeenreset.
An exit command (or a return command executed at the outermost
function level of a script) encountered in try-list does not
cause the execution of always-list. Instead, the shell exits
immediately after any EXIT trap has been executed.
functionword ... [ () ] [ term ] {list}word ... () [ term ] {list}word ... () [ term ] command
where term is one or more newline or ;. Define a function which
is referenced by any one of word. Normally, only one word is
provided; multiple words are usually only useful for setting
traps. The body of the function is the list between the { and
}. See the section `Functions'.
If the option SH_GLOB is set for compatibility with other
shells, then whitespace may appear between between the left and
right parentheses when there is a single word; otherwise, the
parentheses will be treated as forming a globbing pattern in
that case.
time [ pipeline ]
The pipeline is executed, and timing statistics are reported on
the standard error in the form specified by the TIMEFMT
parameter. If pipeline is omitted, print statistics about the
shell process and its children.
[[exp]]
Evaluates the conditional expression exp and return a zero exit
status if it is true. See the section `Conditional Expressions'
for a description of exp.

ALTERNATEFORMSFORCOMPLEXCOMMANDS

Many of zsh's complex commands have alternate forms. These are
non-standard and are likely not to be obvious even to seasoned shell
programmers; they should not be used anywhere that portability of shell
code is a concern.
The short versions below only work if sublist is of the form `{list}'
or if the SHORT_LOOPS option is set. For the if, while and until
commands, in both these cases the test part of the loop must also be
suitably delimited, such as by `[[...]]' or `((...))', else the end
of the test will not be recognized. For the for, repeat, case and
select commands no such special form for the arguments is necessary,
but the other condition (the special form of sublist or use of the
SHORT_LOOPS option) still applies.
iflist{list} [ eliflist{list} ] ... [ else{list} ]
An alternate form of if. The rules mean that
if[[-oignorebraces]]{printyes}
works, but
iftrue{#Doesnotwork!printyes}
does not, since the test is not suitably delimited.
iflistsublist
A short form of the alternate `if'. The same limitations on the
form of list apply as for the previous form.
forname ... (word ... )sublist
A short form of for.
forname ... [ inword ... ] termsublist
where term is at least one newline or ;. Another short form of
for.
for(( [expr1] ; [expr2] ; [expr3] ))sublist
A short form of the arithmetic for command.
foreachname ... (word ... )listend
Another form of for.
whilelist{list}
An alternative form of while. Note the limitations on the form
of list mentioned above.
untillist{list}
An alternative form of until. Note the limitations on the form
of list mentioned above.
repeatwordsublist
This is a short form of repeat.
caseword{ [ [(] pattern [ |pattern ] ... )list (;;|;&|;|) ] ... }
An alternative form of case.
selectname [ inwordterm ] sublist
where term is at least one newline or ;. A short form of
select.

RESERVEDWORDS

The following words are recognized as reserved words when used as the
first word of a command unless quoted or disabled using disable-r:
dodoneesacthenelifelsefiforcaseifwhilefunctionrepeattimeuntilselectcoprocnocorrectforeachend![[{}
Additionally, `}' is recognized in any position if neither the
IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.

COMMENTS

In non-interactive shells, or in interactive shells with the
INTERACTIVE_COMMENTS option set, a word beginning with the third
character of the histchars parameter (`#' by default) causes that word
and all the following characters up to a newline to be ignored.

ALIASING

Every token in the shell input is checked to see if there is an alias
defined for it. If so, it is replaced by the text of the alias if it
is in command position (if it could be the first word of a simple
command), or if the alias is global. If the text ends with a space,
the next word in the shell input is treated as though it were in
command position for purposes of alias expansion. An alias is defined
using the alias builtin; global aliases may be defined using the -g
option to that builtin.
Alias expansion is done on the shell input before any other expansion
except history expansion. Therefore, if an alias is defined for the
word foo, alias expansion may be avoided by quoting part of the word,
e.g. \foo. Any form of quoting works, although there is nothing to
prevent an alias being defined for the quoted form such as \foo as
well. For use with completion, which would remove an initial backslash
followed by a character that isn't special, it may be more convenient
to quote the word by starting with a single quote, i.e. 'foo;
completion will automatically add the trailing single quote.
There is a commonly encountered problem with aliases illustrated by the
following code:
aliasechobar='echobar';echobar
This prints a message that the command echobar could not be found.
This happens because aliases are expanded when the code is read in; the
entire line is read in one go, so that when echobar is executed it is
too late to expand the newly defined alias. This is often a problem in
shell scripts, functions, and code executed with `source' or `.'.
Consequently, use of functions rather than aliases is recommended in
non-interactive code.
Note also the unhelpful interaction of aliases and function
definitions:
aliasfunc='noglobfunc'func(){echoDosomethingwith$*}
Because aliases are expanded in function definitions, this causes the
following command to be executed:
noglobfunc(){echoDosomethingwith$*}
which defines noglob as well as func as functions with the body given.
To avoid this, either quote the name func or use the alternative
function definition form `functionfunc'. Ensuring the alias is
defined after the function works but is problematic if the code
fragment might be re-executed.

QUOTING

A character may be quoted (that is, made to stand for itself) by
preceding it with a `\'. `\' followed by a newline is ignored.
A string enclosed between `$'' and `'' is processed the same way as the
string arguments of the print builtin, and the resulting string is
considered to be entirely quoted. A literal `'' character can be
included in the string by using the `\'' escape.
All characters enclosed between a pair of single quotes ('') that is
not preceded by a `$' are quoted. A single quote cannot appear within
single quotes unless the option RC_QUOTES is set, in which case a pair
of single quotes are turned into a single quote. For example,
print''''
outputs nothing apart from a newline if RC_QUOTES is not set, but one
single quote if it is set.
Inside double quotes (""), parameter and command substitution occur,
and `\' quotes the characters `\', ``', `"', and `$'.

REDIRECTION

If a command is followed by & and job control is not active, then the
default standard input for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by input/output
specifications.
The following may appear anywhere in a simple command or may precede or
follow a complex command. Expansion occurs before word or digit is
used except as noted below. If the result of substitution on word
produces more than one filename, redirection occurs for each separate
filename in turn.
<word Open file word for reading as standard input.
<>word
Open file word for reading and writing as standard input. If
the file does not exist then it is created.
>word Open file word for writing as standard output. If the file does
not exist then it is created. If the file exists, and the
CLOBBER option is unset, this causes an error; otherwise, it is
truncated to zero length.
>|word>!word
Same as >, except that the file is truncated to zero length if
it exists, even if CLOBBER is unset.
>>word
Open file word for writing in append mode as standard output.
If the file does not exist, and the CLOBBER option is unset,
this causes an error; otherwise, the file is created.
>>|word>>!word
Same as >>, except that the file is created if it does not
exist, even if CLOBBER is unset.
<<[-] word
The shell input is read up to a line that is the same as word,
or to an end-of-file. No parameter expansion, command
substitution or filename generation is performed on word. The
resulting document, called a here-document, becomes the standard
input.
If any character of word is quoted with single or double quotes
or a `\', no interpretation is placed upon the characters of the
document. Otherwise, parameter and command substitution occurs,
`\' followed by a newline is removed, and `\' must be used to
quote the characters `\', `$', ``' and the first character of
word.
Note that word itself does not undergo shell expansion.
Backquotes in word do not have their usual effect; instead they
behave similarly to double quotes, except that the backquotes
themselves are passed through unchanged. (This information is
given for completeness and it is not recommended that backquotes
be used.) Quotes in the form $'...' have their standard effect
of expanding backslashed references to special characters.
If <<- is used, then all leading tabs are stripped from word and
from the document.
<<<word
Perform shell expansion on word and pass the result to standard
input. This is known as a here-string. Compare the use of word
in here-documents above, where word does not undergo shell
expansion.
<&number>&number
The standard input/output is duplicated from file descriptor
number (see dup2(2)).
<&->&- Close the standard input/output.
<&p>&p The input/output from/to the coprocess is moved to the standard
input/output.
>&word&>word
(Except where `>&word' matches one of the above syntaxes; `&>'
can always be used to avoid this ambiguity.) Redirects both
standard output and standard error (file descriptor 2) in the
manner of `>word'. Note that this does not have the same
effect as `>word2>&1' in the presence of multios (see the
section below).
>&|word>&!word&>|word&>!word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>|word'.
>>&word&>>word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>>word'.
>>&|word>>&!word&>>|word&>>!word
Redirects both standard output and standard error (file
descriptor 2) in the manner of `>>|word'.
If one of the above is preceded by a digit, then the file descriptor
referred to is that specified by the digit instead of the default 0 or
1. The order in which redirections are specified is significant. The
shell evaluates each redirection in terms of the (filedescriptor,
file) association at the time of evaluation. For example:
... 1>fname2>&1
first associates file descriptor 1 with file fname. It then associates
file descriptor 2 with the file associated with file descriptor 1 (that
is, fname). If the order of redirections were reversed, file
descriptor 2 would be associated with the terminal (assuming file
descriptor 1 had been) and then file descriptor 1 would be associated
with file fname.
The `|&' command separator described in SimpleCommands&Pipelines in
zshmisc(1) is a shorthand for `2>&1|'.
The various forms of process substitution, `<(list)', and `=(list())'
for input and `>(list)' for output, are often used together with
redirection. For example, if word in an output redirection is of the
form `>(list)' then the output is piped to the command represented by
list. See ProcessSubstitution in zshexpn(1).

OPENINGFILEDESCRIPTORSUSINGPARAMETERS

When the shell is parsing arguments to a command, and the shell option
IGNORE_BRACES is not set, a different form of redirection is allowed:
instead of a digit before the operator there is a valid shell
identifier enclosed in braces. The shell will open a new file
descriptor that is guaranteed to be at least 10 and set the parameter
named by the identifier to the file descriptor opened. No whitespace
is allowed between the closing brace and the redirection character.
For example:
... {myfd}>&1
This opens a new file descriptor that is a duplicate of file descriptor
1 and sets the parameter myfd to the number of the file descriptor,
which will be at least 10. The new file descriptor can be written to
using the syntax >&$myfd.
The syntax {varid}>&-, for example {myfd}>&-, may be used to close a
file descriptor opened in this fashion. Note that the parameter given
by varid must previously be set to a file descriptor in this case.
It is an error to open or close a file descriptor in this fashion when
the parameter is readonly. However, it is not an error to read or
write a file descriptor using <&$param or >&$param if param is
readonly.
If the option CLOBBER is unset, it is an error to open a file
descriptor using a parameter that is already set to an open file
descriptor previously allocated by this mechanism. Unsetting the
parameter before using it for allocating a file descriptor avoids the
error.
Note that this mechanism merely allocates or closes a file descriptor;
it does not perform any redirections from or to it. It is usually
convenient to allocate a file descriptor prior to use as an argument to
exec. The syntax does not in any case work when used around complex
commands such as parenthesised subshells or loops, where the opening
brace is interpreted as part of a command list to be executed in the
current shell.
The following shows a typical sequence of allocation, use, and closing
of a file descriptor:
integermyfdexec{myfd}>~/logs/mylogfile.txtprintThisisalogmessage.>&$myfdexec{myfd}>&-
Note that the expansion of the variable in the expression >&$myfd
occurs at the point the redirection is opened. This is after the
expansion of command arguments and after any redirections to the left
on the command line have been processed.

MULTIOS

If the user tries to open a file descriptor for writing more than once,
the shell opens the file descriptor as a pipe to a process that copies
its input to all the specified outputs, similar to tee, provided the
MULTIOS option is set, as it is by default. Thus:
date>foo>bar
writes the date to two files, named `foo' and `bar'. Note that a pipe
is an implicit redirection; thus
date>foo|cat
writes the date to the file `foo', and also pipes it to cat.
If the MULTIOS option is set, the word after a redirection operator is
also subjected to filename generation (globbing). Thus
:>*
will truncate all files in the current directory, assuming there's at
least one. (Without the MULTIOS option, it would create an empty file
called `*'.) Similarly, you can do
echoexit0>>*.sh
If the user tries to open a file descriptor for reading more than once,
the shell opens the file descriptor as a pipe to a process that copies
all the specified inputs to its output in the order specified, similar
to cat, provided the MULTIOS option is set. Thus
sort<foo<fubar
or even
sort<f{oo,ubar}
is equivalent to `catfoofubar|sort'.
Expansion of the redirection argument occurs at the point the
redirection is opened, at the point described above for the expansion
of the variable in >&$myfd.
Note that a pipe is an implicit redirection; thus
catbar|sort<foo
is equivalent to `catbarfoo|sort' (note the order of the inputs).
If the MULTIOS option is unset, each redirection replaces the previous
redirection for that file descriptor. However, all files redirected to
are actually opened, so
echofoo>bar>baz
when MULTIOS is unset will truncate bar, and write `foo' into baz.
There is a problem when an output multio is attached to an external
program. A simple example shows this:
catfile>file1>file2catfile1file2
Here, it is possible that the second `cat' will not display the full
contents of file1 and file2 (i.e. the original contents of file
repeated twice).
The reason for this is that the multios are spawned after the cat
process is forked from the parent shell, so the parent shell does not
wait for the multios to finish writing data. This means the command as
shown can exit before file1 and file2 are completely written. As a
workaround, it is possible to run the cat process as part of a job in
the current shell:
{catfile}>file>file2
Here, the {...} job will pause to wait for both files to be written.

REDIRECTIONSWITHNOCOMMAND

When a simple command consists of one or more redirection operators and
zero or more parameter assignments, but no command name, zsh can behave
in several ways.
If the parameter NULLCMD is not set or the option CSH_NULLCMD is set,
an error is caused. This is the csh behavior and CSH_NULLCMD is set by
default when emulating csh.
If the option SH_NULLCMD is set, the builtin `:' is inserted as a
command with the given redirections. This is the default when
emulating sh or ksh.
Otherwise, if the parameter NULLCMD is set, its value will be used as a
command with the given redirections. If both NULLCMD and READNULLCMD
are set, then the value of the latter will be used instead of that of
the former when the redirection is an input. The default for NULLCMD
is `cat' and for READNULLCMD is `more'. Thus
<file
shows the contents of file on standard output, with paging if that is a
terminal. NULLCMD and READNULLCMD may refer to shell functions.

COMMANDEXECUTION

If a command name contains no slashes, the shell attempts to locate it.
If there exists a shell function by that name, the function is invoked
as described in the section `Functions'. If there exists a shell
builtin by that name, the builtin is invoked.
Otherwise, the shell searches each element of $path for a directory
containing an executable file by that name. If the search is
unsuccessful, the shell prints an error message and returns a nonzero
exit status.
If execution fails because the file is not in executable format, and
the file is not a directory, it is assumed to be a shell script.
/bin/sh is spawned to execute it. If the program is a file beginning
with `#!', the remainder of the first line specifies an interpreter for
the program. The shell will execute the specified interpreter on
operating systems that do not handle this executable format in the
kernel.
If no external command is found but a function
command_not_found_handler exists the shell executes this function with
all command line arguments. The function should return status zero if
it successfully handled the command, or non-zero status if it failed.
In the latter case the standard handling is applied: `command not
found' is printed to standard error and the shell exits with status
127. Note that the handler is executed in a subshell forked to execute
an external command, hence changes to directories, shell parameters,
etc. have no effect on the main shell.

FUNCTIONS

Shell functions are defined with the function reserved word or the
special syntax `funcname()'. Shell functions are read in and stored
internally. Alias names are resolved when the function is read.
Functions are executed like commands with the arguments passed as
positional parameters. (See the section `Command Execution'.)
Functions execute in the same process as the caller and share all files
and present working directory with the caller. A trap on EXIT set
inside a function is executed after the function completes in the
environment of the caller.
The return builtin is used to return from function calls.
Function identifiers can be listed with the functions builtin.
Functions can be undefined with the unfunction builtin.

AUTOLOADINGFUNCTIONS

A function can be marked as undefined using the autoload builtin (or
`functions-u' or `typeset-fu'). Such a function has no body. When
the function is first executed, the shell searches for its definition
using the elements of the fpath variable. Thus to define functions for
autoloading, a typical sequence is:
fpath=(~/myfuncs$fpath)autoloadmyfunc1myfunc2...
The usual alias expansion during reading will be suppressed if the
autoload builtin or its equivalent is given the option -U. This is
recommended for the use of functions supplied with the zsh
distribution. Note that for functions precompiled with the zcompile
builtin command the flag -U must be provided when the .zwc file is
created, as the corresponding information is compiled into the latter.
For each element in fpath, the shell looks for three possible files,
the newest of which is used to load the definition for the function:
element.zwc
A file created with the zcompile builtin command, which is
expected to contain the definitions for all functions in the
directory named element. The file is treated in the same manner
as a directory containing files for functions and is searched
for the definition of the function. If the definition is not
found, the search for a definition proceeds with the other two
possibilities described below.
If element already includes a .zwc extension (i.e. the extension
was explicitly given by the user), element is searched for the
definition of the function without comparing its age to that of
other files; in fact, there does not need to be any directory
named element without the suffix. Thus including an element
such as `/usr/local/funcs.zwc' in fpath will speed up the search
for functions, with the disadvantage that functions included
must be explicitly recompiled by hand before the shell notices
any changes.
element/function.zwc
A file created with zcompile, which is expected to contain the
definition for function. It may include other function
definitions as well, but those are neither loaded nor executed;
a file found in this way is searched only for the definition of
function.
element/function
A file of zsh command text, taken to be the definition for
function.
In summary, the order of searching is, first, in the parentsof
directories in fpath for the newer of either a compiled directory or a
directory in fpath; second, if more than one of these contains a
definition for the function that is sought, the leftmost in the fpath
is chosen; and third, within a directory, the newer of either a
compiled function or an ordinary function definition is used.
If the KSH_AUTOLOAD option is set, or the file contains only a simple
definition of the function, the file's contents will be executed. This
will normally define the function in question, but may also perform
initialization, which is executed in the context of the function
execution, and may therefore define local parameters. It is an error
if the function is not defined by loading the file.
Otherwise, the function body (with no surrounding `funcname(){...}')
is taken to be the complete contents of the file. This form allows the
file to be used directly as an executable shell script. If processing
of the file results in the function being re-defined, the function
itself is not re-executed. To force the shell to perform
initialization and then call the function defined, the file should
contain initialization code (which will be executed then discarded) in
addition to a complete function definition (which will be retained for
subsequent calls to the function), and a call to the shell function,
including any arguments, at the end.
For example, suppose the autoload file func contains
func(){printThisisfunc;}printfuncisinitialized
then `func;func' with KSH_AUTOLOAD set will produce both messages on
the first call, but only the message `Thisisfunc' on the second and
subsequent calls. Without KSH_AUTOLOAD set, it will produce the
initialization message on the first call, and the other message on the
second and subsequent calls.
It is also possible to create a function that is not marked as
autoloaded, but which loads its own definition by searching fpath, by
using `autoload-X' within a shell function. For example, the
following are equivalent:
myfunc(){autoload-X}myfuncargs...
and
unfunctionmyfunc#ifmyfuncwasdefinedautoloadmyfuncmyfuncargs...
In fact, the functions command outputs `builtinautoload-X' as the
body of an autoloaded function. This is done so that
eval"$(functions)"
produces a reasonable result. A true autoloaded function can be
identified by the presence of the comment `#undefined' in the body,
because all comments are discarded from defined functions.
To load the definition of an autoloaded function myfunc without
executing myfunc, use:
autoload+Xmyfunc

ANONYMOUSFUNCTIONS

If no name is given for a function, it is `anonymous' and is handled
specially. Either form of function definition may be used: a `()' with
no preceding name, or a `function' with an immediately following open
brace. The function is executed immediately at the point of definition
and is not stored for future use. The function name is set to
`(anon)'.
Arguments to the function may be specified as words following the
closing brace defining the function, hence if there are none no
arguments (other than $0) are set. This is a difference from the way
other functions are parsed: normal function definitions may be followed
by certain keywords such as `else' or `fi', which will be treated as
arguments to anonymous functions, so that a newline or semicolon is
needed to force keyword interpretation.
Note also that the argument list of any enclosing script or function is
hidden (as would be the case for any other function called at this
point).
Redirections may be applied to the anonymous function in the same
manner as to a current-shell structure enclosed in braces. The main
use of anonymous functions is to provide a scope for local variables.
This is particularly convenient in start-up files as these do not
provide their own local variable scope.
For example,
variable=outsidefunction{localvariable=insideprint"Iam$variablewitharguments$*"}thisandthatprint"Iam$variable"
outputs the following:
IaminsidewithargumentsthisandthatIamoutside
Note that function definitions with arguments that expand to nothing,
for example `name=;function$name{...}', are not treated as
anonymous functions. Instead, they are treated as normal function
definitions where the definition is silently discarded.

SPECIALFUNCTIONS

Certain functions, if defined, have special meaning to the shell.
HookFunctions
For the functions below, it is possible to define an array that has the
same name as the function with `_functions' appended. Any element in
such an array is taken as the name of a function to execute; it is
executed in the same context and with the same arguments as the basic
function. For example, if $chpwd_functions is an array containing the
values `mychpwd', `chpwd_save_dirstack', then the shell attempts to
execute the functions `chpwd', `mychpwd' and `chpwd_save_dirstack', in
that order. Any function that does not exist is silently ignored. A
function found by this mechanism is referred to elsewhere as a `hook
function'. An error in any function causes subsequent functions not to
be run. Note further that an error in a precmd hook causes an
immediately following periodic function not to run (though it may run
at the next opportunity).
chpwd Executed whenever the current working directory is changed.
periodic
If the parameter PERIOD is set, this function is executed every
$PERIOD seconds, just before a prompt. Note that if multiple
functions are defined using the array periodic_functions only
one period is applied to the complete set of functions, and the
scheduled time is not reset if the list of functions is altered.
Hence the set of functions is always called together.
precmd Executed before each prompt. Note that precommand functions are
not re-executed simply because the command line is redrawn, as
happens, for example, when a notification about an exiting job
is displayed.
preexec
Executed just after a command has been read and is about to be
executed. If the history mechanism is active (and the line was
not discarded from the history buffer), the string that the user
typed is passed as the first argument, otherwise it is an empty
string. The actual command that will be executed (including
expanded aliases) is passed in two different forms: the second
argument is a single-line, size-limited version of the command
(with things like function bodies elided); the third argument
contains the full text that is being executed.
zshaddhistory
Executed when a history line has been read interactively, but
before it is executed. The sole argument is the complete
history line (so that any terminating newline will still be
present).
If any of the hook functions return a non-zero value the history
line will not be saved, although it lingers in the history until
the next line is executed allow you to reuse or edit it
immediately.
A hook function may call `fc-p...' to switch the history
context so that the history is saved in a different file from
the that in the global HISTFILE parameter. This is handled
specially: the history context is automatically restored after
the processing of the history line is finished.
The following example function first adds the history line to
the normal history with the newline stripped, which is usually
the correct behaviour. Then it switches the history context so
that the line will be written to a history file in the current
directory.
zshaddhistory(){print-sr--${1%%$'\n'}fc-p.zsh_local_history}zshexit
Executed at the point where the main shell is about to exit
normally. This is not called by exiting subshells, nor when the
exec precommand modifier is used before an external command.
Also, unlike TRAPEXIT, it is not called when functions exit.
TrapFunctions
The functions below are treated specially but do not have corresponding
hook arrays.
TRAPNAL
If defined and non-null, this function will be executed whenever
the shell catches a signal SIGNAL, where NAL is a signal name as
specified for the kill builtin. The signal number will be
passed as the first parameter to the function.
If a function of this form is defined and null, the shell and
processes spawned by it will ignore SIGNAL.
The return status from the function is handled specially. If it
is zero, the signal is assumed to have been handled, and
execution continues normally. Otherwise, the shell will behave
as interrupted except that the return status of the trap is
retained.
Programs terminated by uncaught signals typically return the
status 128 plus the signal number. Hence the following causes
the handler for SIGINT to print a message, then mimic the usual
effect of the signal.
TRAPINT(){print"CaughtSIGINT,aborting."return$((128+$1))}
The functions TRAPZERR, TRAPDEBUG and TRAPEXIT are never
executed inside other traps.
TRAPDEBUG
If the option DEBUG_BEFORE_CMD is set (as it is by default),
executed before each command; otherwise executed after each
command. See the description of the trap builtin in
zshbuiltins(1) for details of additional features provided in
debug traps.
TRAPEXIT
Executed when the shell exits, or when the current function
exits if defined inside a function. The value of $? at the
start of execution is the exit status of the shell or the return
status of the function exiting.
TRAPZERR
Executed whenever a command has a non-zero exit status.
However, the function is not executed if the command occurred in
a sublist followed by `&&' or `||'; only the final command in a
sublist of this type causes the trap to be executed. The
function TRAPERR acts the same as TRAPZERR on systems where
there is no SIGERR (this is the usual case).
The functions beginning `TRAP' may alternatively be defined with the
trap builtin: this may be preferable for some uses. Setting a trap
with one form removes any trap of the other form for the same signal;
removing a trap in either form removes all traps for the same signal.
The forms
TRAPNAL(){#code}
('function traps') and
trap'#code'NAL
('list traps') are equivalent in most ways, the exceptions being the
following:
· Function traps have all the properties of normal functions,
appearing in the list of functions and being called with their
own function context rather than the context where the trap was
triggered.
· The return status from function traps is special, whereas a
return from a list trap causes the surrounding context to return
with the given status.
· Function traps are not reset within subshells, in accordance
with zsh behaviour; list traps are reset, in accordance with
POSIX behaviour.

JOBS

If the MONITOR option is set, an interactive shell associates a job
with each pipeline. It keeps a table of current jobs, printed by the
jobs command, and assigns them small integer numbers. When a job is
started asynchronously with `&', the shell prints a line to standard
error which looks like:
[1]1234
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
If a job is started with `&|' or `&!', then that job is immediately
disowned. After startup, it does not have a place in the job table,
and is not subject to the job control features described here.
If you are running a job and wish to do something else you may hit the
key ^Z (control-Z) which sends a TSTP signal to the current job: this
key may be redefined by the susp option of the external stty command.
The shell will then normally indicate that the job has been
`suspended', and print another prompt. You can then manipulate the
state of this job, putting it in the background with the bg command, or
run some other commands and then eventually bring the job back into the
foreground with the foreground command fg. A ^Z takes effect
immediately and is like an interrupt in that pending output and unread
input are discarded when it is typed.
A job being run in the background will suspend if it tries to read from
the terminal.
Note that if the job running in the foreground is a shell function,
then suspending it will have the effect of causing the shell to fork.
This is necessary to separate the function's state from that of the
parent shell performing the job control, so that the latter can return
to the command line prompt. As a result, even if fg is used to
continue the job the function will no longer be part of the parent
shell, and any variables set by the function will not be visible in the
parent shell. Thus the behaviour is different from the case where the
function was never suspended. Zsh is different from many other shells
in this regard.
The same behaviour is found when the shell is executing code as the
right hand side of a pipeline or any complex shell construct such as
if, for, etc., in order that the entire block of code can be managed as
a single job. Background jobs are normally allowed to produce output,
but this can be disabled by giving the command `sttytostop'. If you
set this tty option, then background jobs will suspend when they try to
produce output like they do when they try to read input.
When a command is suspended and continued later with the fg or wait
builtins, zsh restores tty modes that were in effect when it was
suspended. This (intentionally) does not apply if the command is
continued via `kill-CONT', nor when it is continued with bg.
There are several ways to refer to jobs in the shell. A job can be
referred to by the process ID of any process of the job or by one of
the following:
%number
The job with the given number.
%string
Any job whose command line begins with string.
%?string
Any job whose command line contains string.
%% Current job.
%+ Equivalent to `%%'.
%- Previous job.
The shell learns immediately whenever a process changes state. It
normally informs you whenever a job becomes blocked so that no further
progress is possible. If the NOTIFY option is not set, it waits until
just before it prints a prompt before it informs you. All such
notifications are sent directly to the terminal, not to the standard
output or standard error.
When the monitor mode is on, each background job that completes
triggers any trap set for CHLD.
When you try to leave the shell while jobs are running or suspended,
you will be warned that `You have suspended (running) jobs'. You may
use the jobs command to see what they are. If you do this or
immediately try to exit again, the shell will not warn you a second
time; the suspended jobs will be terminated, and the running jobs will
be sent a SIGHUP signal, if the HUP option is set.
To avoid having the shell terminate the running jobs, either use the
nohup command (see nohup(1)) or the disown builtin.

SIGNALS

The INT and QUIT signals for an invoked command are ignored if the
command is followed by `&' and the MONITOR option is not active. The
shell itself always ignores the QUIT signal. Otherwise, signals have
the values inherited by the shell from its parent (but see the TRAPNAL
special functions in the section `Functions').

ARITHMETICEVALUATION

The shell can perform integer and floating point arithmetic, either
using the builtin let, or via a substitution of the form $((...)). For
integers, the shell is usually compiled to use 8-byte precision where
this is available, otherwise precision is 4 bytes. This can be tested,
for example, by giving the command `print-$((12345678901))'; if the
number appears unchanged, the precision is at least 8 bytes. Floating
point arithmetic always uses the `double' type with whatever
corresponding precision is provided by the compiler and the library.
The let builtin command takes arithmetic expressions as arguments; each
is evaluated separately. Since many of the arithmetic operators, as
well as spaces, require quoting, an alternative form is provided: for
any command which begins with a `((', all the characters until a
matching `))' are treated as a quoted expression and arithmetic
expansion performed as for an argument of let. More precisely,
`((...))' is equivalent to `let"..."'. The return status is 0 if the
arithmetic value of the expression is non-zero, 1 if it is zero, and 2
if an error occurred.
For example, the following statement
((val=2+1))
is equivalent to
let"val=2+1"
both assigning the value 3 to the shell variable val and returning a
zero status.
Integers can be in bases other than 10. A leading `0x' or `0X' denotes
hexadecimal. Integers may also be of the form `base#n', where base is
a decimal number between two and thirty-six representing the arithmetic
base and n is a number in that base (for example, `16#ff' is 255 in
hexadecimal). The base# may also be omitted, in which case base 10 is
used. For backwards compatibility the form `[base]n' is also accepted.
It is also possible to specify a base to be used for output in the form
`[#base]', for example `[#16]'. This is used when outputting
arithmetical substitutions or when assigning to scalar parameters, but
an explicitly defined integer or floating point parameter will not be
affected. If an integer variable is implicitly defined by an
arithmetic expression, any base specified in this way will be set as
the variable's output arithmetic base as if the option `-ibase' to the
typeset builtin had been used. The expression has no precedence and if
it occurs more than once in a mathematical expression, the last
encountered is used. For clarity it is recommended that it appear at
the beginning of an expression. As an example:
typeset-i16yprint$(([#8]x=32,y=32))print$x$y
outputs first `8#40', the rightmost value in the given output base, and
then `8#4016#20', because y has been explicitly declared to have
output base 16, while x (assuming it does not already exist) is
implicitly typed by the arithmetic evaluation, where it acquires the
output base 8.
If the C_BASES option is set, hexadecimal numbers in the standard C
format, for example 0xFF instead of the usual `16#FF'. If the option
OCTAL_ZEROES is also set (it is not by default), octal numbers will be
treated similarly and hence appear as `077' instead of `8#77'. This
option has no effect on the output of bases other than hexadecimal and
octal, and these formats are always understood on input.
When an output base is specified using the `[#base]' syntax, an
appropriate base prefix will be output if necessary, so that the value
output is valid syntax for input. If the # is doubled, for example
`[##16]', then no base prefix is output.
Floating point constants are recognized by the presence of a decimal
point or an exponent. The decimal point may be the first character of
the constant, but the exponent character e or E may not, as it will be
taken for a parameter name.
An arithmetic expression uses nearly the same syntax and associativity
of expressions as in C.
In the native mode of operation, the following operators are supported
(listed in decreasing order of precedence):
+-!~++--
unary plus/minus, logical NOT, complement,
{pre,post}{in,de}crement
<<>> bitwise shift left, right
& bitwise AND
^ bitwise XOR
| bitwise OR
** exponentiation
*/% multiplication, division, modulus (remainder)
+- addition, subtraction
<><=>=
comparison
==!= equality and inequality
&& logical AND
||^^ logical OR, XOR
?: ternary operator
=+=-=*=/=%=&=^=|=<<=>>=&&=||=^^=**=
assignment
, comma operator
The operators `&&', `||', `&&=', and `||=' are short-circuiting, and
only one of the latter two expressions in a ternary operator is
evaluated. Note the precedence of the bitwise AND, OR, and XOR
operators.
With the option C_PRECEDENCES the precedences (but no other properties)
of the operators are altered to be the same as those in most other
languages that support the relevant operators:
+-!~++--
unary plus/minus, logical NOT, complement,
{pre,post}{in,de}crement
** exponentiation
*/% multiplication, division, modulus (remainder)
+- addition, subtraction
<<>> bitwise shift left, right
<><=>=
comparison
==!= equality and inequality
& bitwise AND
^ bitwise XOR
| bitwise OR
&& logical AND
^^ logical XOR
|| logical OR
?: ternary operator
=+=-=*=/=%=&=^=|=<<=>>=&&=||=^^=**=
assignment
, comma operator
Note the precedence of exponentiation in both cases is below that of
unary operators, hence `-3**2' evaluates as `9', not -9. Use
parentheses where necessary: `-(3**2)'. This is for compatibility with
other shells.
Mathematical functions can be called with the syntax `func(args)',
where the function decides if the args is used as a string or a
comma-separated list of arithmetic expressions. The shell currently
defines no mathematical functions by default, but the module
zsh/mathfunc may be loaded with the zmodload builtin to provide
standard floating point mathematical functions.
An expression of the form `##x' where x is any character sequence such
as `a', `^A', or `\M-\C-x' gives the value of this character and an
expression of the form `#foo' gives the value of the first character of
the contents of the parameter foo. Character values are according to
the character set used in the current locale; for multibyte character
handling the option MULTIBYTE must be set. Note that this form is
different from `$#foo', a standard parameter substitution which gives
the length of the parameter foo. `#\' is accepted instead of `##', but
its use is deprecated.
Named parameters and subscripted arrays can be referenced by name
within an arithmetic expression without using the parameter expansion
syntax. For example,
((val2=val1*2))
assigns twice the value of $val1 to the parameter named val2.
An internal integer representation of a named parameter can be
specified with the integer builtin. Arithmetic evaluation is performed
on the value of each assignment to a named parameter declared integer
in this manner. Assigning a floating point number to an integer
results in rounding down to the next integer.
Likewise, floating point numbers can be declared with the float
builtin; there are two types, differing only in their output format, as
described for the typeset builtin. The output format can be bypassed
by using arithmetic substitution instead of the parameter substitution,
i.e. `${float}' uses the defined format, but `$((float))' uses a
generic floating point format.
Promotion of integer to floating point values is performed where
necessary. In addition, if any operator which requires an integer
(`~', `&', `|', `^', `%', `<<', `>>' and their equivalents with
assignment) is given a floating point argument, it will be silently
rounded down to the next integer.
Scalar variables can hold integer or floating point values at different
times; there is no memory of the numeric type in this case.
If a variable is first assigned in a numeric context without previously
being declared, it will be implicitly typed as integer or float and
retain that type either until the type is explicitly changed or until
the end of the scope. This can have unforeseen consequences. For
example, in the loop
for((f=0;f<1;f+=0.1));do#use$fdone
if f has not already been declared, the first assignment will cause it
to be created as an integer, and consequently the operation `f+=0.1'
will always cause the result to be truncated to zero, so that the loop
will fail. A simple fix would be to turn the initialization into `f=0.0'. It is therefore best to declare numeric variables with explicit
types.

CONDITIONALEXPRESSIONS

A conditionalexpression is used with the [[ compound command to test
attributes of files and to compare strings. Each expression can be
constructed from one or more of the following unary or binary
expressions:
-afile
true if file exists.
-bfile
true if file exists and is a block special file.
-cfile
true if file exists and is a character special file.
-dfile
true if file exists and is a directory.
-efile
true if file exists.
-ffile
true if file exists and is a regular file.
-gfile
true if file exists and has its setgid bit set.
-hfile
true if file exists and is a symbolic link.
-kfile
true if file exists and has its sticky bit set.
-nstring
true if length of string is non-zero.
-ooption
true if option named option is on. option may be a single
character, in which case it is a single letter option name.
(See the section `Specifying Options'.)
-pfile
true if file exists and is a FIFO special file (named pipe).
-rfile
true if file exists and is readable by current process.
-sfile
true if file exists and has size greater than zero.
-tfd true if file descriptor number fd is open and associated with a
terminal device. (note: fd is not optional)
-ufile
true if file exists and has its setuid bit set.
-wfile
true if file exists and is writable by current process.
-xfile
true if file exists and is executable by current process. If
file exists and is a directory, then the current process has
permission to search in the directory.
-zstring
true if length of string is zero.
-Lfile
true if file exists and is a symbolic link.
-Ofile
true if file exists and is owned by the effective user ID of
this process.
-Gfile
true if file exists and its group matches the effective group ID
of this process.
-Sfile
true if file exists and is a socket.
-Nfile
true if file exists and its access time is not newer than its
modification time.
file1-ntfile2
true if file1 exists and is newer than file2.
file1-otfile2
true if file1 exists and is older than file2.
file1-effile2
true if file1 and file2 exist and refer to the same file.
string=patternstring==pattern
true if string matches pattern. The `==' form is the preferred
one. The `=' form is for backward compatibility and should be
considered obsolete.
string!=pattern
true if string does not match pattern.
string=~regexp
true if string matches the regular expression regexp. If the
option RE_MATCH_PCRE is set regexp is tested as a PCRE regular
expression using the zsh/pcre module, else it is tested as a
POSIX extended regular expression using the zsh/regex module.
Upon successful match, some variables will be updated; no
variables are changed if the matching fails.
If the option BASH_REMATCH is not set the scalar parameter MATCH
is set to the substring that matched the pattern and the integer
parameters MBEGIN and MEND to the index of the start and end,
respectively, of the match in string, such that if string is
contained in variable var the expression `${var[$MBEGIN,$MEND]}'
is identical to `$MATCH'. The setting of the option KSH_ARRAYS
is respected. Likewise, the array match is set to the
substrings that matched parenthesised subexpressions and the
arrays mbegin and mend to the indices of the start and end
positions, respectively, of the substrings within string. The
arrays are not set if there were no parenthesised
subexpresssions. For example, if the string `ashortstring' is
matched against the regular expression `s(...)t', then (assuming
the option KSH_ARRAYS is not set) MATCH, MBEGIN and MEND are
`short', 3 and 7, respectively, while match, mbegin and mend are
single entry arrays containing the strings `hor', `4' and `6,
respectively.
If the option BASH_REMATCH is set the array BASH_REMATCH is set
to the substring that matched the pattern followed by the
substrings that matched parenthesised subexpressions within the
pattern.
string1<string2
true if string1 comes before string2 based on ASCII value of
their characters.
string1>string2
true if string1 comes after string2 based on ASCII value of
their characters.
exp1-eqexp2
true if exp1 is numerically equal to exp2.
exp1-neexp2
true if exp1 is numerically not equal to exp2.
exp1-ltexp2
true if exp1 is numerically less than exp2.
exp1-gtexp2
true if exp1 is numerically greater than exp2.
exp1-leexp2
true if exp1 is numerically less than or equal to exp2.
exp1-geexp2
true if exp1 is numerically greater than or equal to exp2.
(exp)
true if exp is true.
!exp true if exp is false.
exp1&&exp2
true if exp1 and exp2 are both true.
exp1||exp2
true if either exp1 or exp2 is true.
Normal shell expansion is performed on the file, string and pattern
arguments, but the result of each expansion is constrained to be a
single word, similar to the effect of double quotes. Filename
generation is not performed on any form of argument to conditions.
However, pattern metacharacters are active for the pattern arguments;
the patterns are the same as those used for filename generation, see
zshexpn(1), but there is no special behaviour of `/' nor initial dots,
and no glob qualifiers are allowed.
In each of the above expressions, if file is of the form `/dev/fd/n',
where n is an integer, then the test applied to the open file whose
descriptor number is n, even if the underlying system does not support
the /dev/fd directory.
In the forms which do numeric comparison, the expressions exp undergo
arithmetic expansion as if they were enclosed in $((...)).
For example, the following:
[[(-ffoo||-fbar)&&$report=y*]]&&printFileexists.
tests if either file foo or file bar exists, and if so, if the value of
the parameter report begins with `y'; if the complete condition is
true, the message `Fileexists.' is printed.

EXPANSIONOFPROMPTSEQUENCES

Prompt sequences undergo a special form of expansion. This type of
expansion is also available using the -P option to the print builtin.
If the PROMPT_SUBST option is set, the prompt string is first subjected
to parameterexpansion, commandsubstitution and arithmeticexpansion.
See zshexpn(1).
Certain escape sequences may be recognised in the prompt string.
If the PROMPT_BANG option is set, a `!' in the prompt is replaced by
the current history event number. A literal `!' may then be
represented as `!!'.
If the PROMPT_PERCENT option is set, certain escape sequences that
start with `%' are expanded. Many escapes are followed by a single
character, although some of these take an optional integer argument
that should appear between the `%' and the next character of the
sequence. More complicated escape sequences are available to provide
conditional expansion.

SIMPLEPROMPTESCAPES

Specialcharacters%% A `%'.
%) A `)'.
Logininformation%l The line (tty) the user is logged in on, without `/dev/' prefix.
If the name starts with `/dev/tty', that prefix is stripped.
%M The full machine hostname.
%m The hostname up to the first `.'. An integer may follow the `%'
to specify how many components of the hostname are desired.
With a negative integer, trailing components of the hostname are
shown.
%n$USERNAME.
%y The line (tty) the user is logged in on, without `/dev/' prefix.
This does not treat `/dev/tty' names specially.
Shellstate%# A `#' if the shell is running with privileges, a `%' if not.
Equivalent to `%(!.#.%%)'. The definition of `privileged', for
these purposes, is that either the effective user ID is zero,
or, if POSIX.1e capabilities are supported, that at least one
capability is raised in either the Effective or Inheritable
capability vectors.
%? The return status of the last command executed just before the
prompt.
%_ The status of the parser, i.e. the shell constructs (like `if'
and `for') that have been started on the command line. If given
an integer number that many strings will be printed; zero or
negative or no integer means print as many as there are. This
is most useful in prompts PS2 for continuation lines and PS4 for
debugging with the XTRACE option; in the latter case it will
also work non-interactively.
%d/ Current working directory. If an integer follows the `%', it
specifies a number of trailing components of the current working
directory to show; zero means the whole path. A negative
integer specifies leading components, i.e. %-1d specifies the
first component.
%~ As %d and %/, but if the current working directory has a named
directory as its prefix, that part is replaced by a `~' followed
by the name of the directory. If it starts with $HOME, that
part is replaced by a `~'.
%h%! Current history event number.
%i The line number currently being executed in the script, sourced
file, or shell function given by %N. This is most useful for
debugging as part of $PS4.
%I The line number currently being executed in the file %x. This
is similar to %i, but the line number is always a line number in
the file where the code was defined, even if the code is a shell
function.
%j The number of jobs.
%L The current value of $SHLVL.
%N The name of the script, sourced file, or shell function that zsh
is currently executing, whichever was started most recently. If
there is none, this is equivalent to the parameter $0. An
integer may follow the `%' to specify a number of trailing path
components to show; zero means the full path. A negative
integer specifies leading components.
%x The name of the file containing the source code currently being
executed. This behaves as %N except that function and eval
command names are not shown, instead the file where they were
defined.
%c%.%C Trailing component of the current working directory. An integer
may follow the `%' to get more than one component. Unless `%C'
is used, tilde contraction is performed first. These are
deprecated as %c and %C are equivalent to %1~ and %1/,
respectively, while explicit positive integers have the same
effect as for the latter two sequences.
Dateandtime%D The date in yy-mm-dd format.
%T Current time of day, in 24-hour format.
%t%@ Current time of day, in 12-hour, am/pm format.
%* Current time of day in 24-hour format, with seconds.
%w The date in day-dd format.
%W The date in mm/dd/yy format.
%D{string}string is formatted using the strftime function. See
strftime(3) for more details. Various zsh extensions provide
numbers with no leading zero or space if the number is a single
digit:
%f a day of the month
%K the hour of the day on the 24-hour clock
%L the hour of the day on the 12-hour clock
The GNU extension that a `-' between the % and the format
character causes a leading zero or space to be stripped is
handled directly by the shell for the format characters d, f, H,
k, l, m, M, S and y; any other format characters are provided to
strftime() with any leading `-', present, so the handling is
system dependent. Further GNU extensions are not supported at
present.
Visualeffects%B (%b)
Start (stop) boldface mode.
%E Clear to end of line.
%U (%u)
Start (stop) underline mode.
%S (%s)
Start (stop) standout mode.
%F (%f)
Start (stop) using a different foreground colour, if supported
by the terminal. The colour may be specified two ways: either
as a numeric argument, as normal, or by a sequence in braces
following the %F, for example %F{red}. In the latter case the
values allowed are as described for the fgzle_highlight
attribute; see CharacterHighlighting in zshzle(1). This means
that numeric colours are allowed in the second format also.
%K (%k)
Start (stop) using a different bacKground colour. The syntax is
identical to that for %F and %f.
%{...%}
Include a string as a literal escape sequence. The string
within the braces should not change the cursor position. Brace
pairs can nest.
A positive numeric argument between the % and the { is treated
as described for %G below.
%G Within a %{...%} sequence, include a `glitch': that is, assume
that a single character width will be output. This is useful
when outputting characters that otherwise cannot be correctly
handled by the shell, such as the alternate character set on
some terminals. The characters in question can be included
within a %{...%} sequence together with the appropriate number
of %G sequences to indicate the correct width. An integer
between the `%' and `G' indicates a character width other than
one. Hence %{seq%2G%} outputs seq and assumes it takes up the
width of two standard characters.
Multiple uses of %G accumulate in the obvious fashion; the
position of the %G is unimportant. Negative integers are not
handled.
Note that when prompt truncation is in use it is advisable to
divide up output into single characters within each %{...%}
group so that the correct truncation point can be found.

CONDITIONALSUBSTRINGSINPROMPTS

%v The value of the first element of the psvar array parameter.
Following the `%' with an integer gives that element of the
array. Negative integers count from the end of the array.
%(x.true-text.false-text)
Specifies a ternary expression. The character following the x
is arbitrary; the same character is used to separate the text
for the `true' result from that for the `false' result. This
separator may not appear in the true-text, except as part of a
%-escape sequence. A `)' may appear in the false-text as `%)'.
true-text and false-text may both contain arbitrarily-nested
escape sequences, including further ternary expressions.
The left parenthesis may be preceded or followed by a positive
integer n, which defaults to zero. A negative integer will be
multiplied by -1. The test character x may be any of the
following:
! True if the shell is running with privileges.
# True if the effective uid of the current process is n.
? True if the exit status of the last command was n.
_ True if at least n shell constructs were started.
C/ True if the current absolute path has at least n elements
relative to the root directory, hence / is counted as 0
elements.
c.~ True if the current path, with prefix replacement, has at
least n elements relative to the root directory, hence /
is counted as 0 elements.
D True if the month is equal to n (January = 0).
d True if the day of the month is equal to n.
g True if the effective gid of the current process is n.
j True if the number of jobs is at least n.
L True if the SHLVL parameter is at least n.
l True if at least n characters have already been printed
on the current line.
S True if the SECONDS parameter is at least n.
T True if the time in hours is equal to n.
t True if the time in minutes is equal to n.
v True if the array psvar has at least n elements.
V True if element n of the array psvar is set and
non-empty.
w True if the day of the week is equal to n (Sunday = 0).
%<string<%>string>%[xstring]
Specifies truncation behaviour for the remainder of the prompt
string. The third, deprecated, form is equivalent to
`%xstringx', i.e. x may be `<' or `>'. The numeric argument,
which in the third form may appear immediately after the `[',
specifies the maximum permitted length of the various strings
that can be displayed in the prompt. The string will be
displayed in place of the truncated portion of any string; note
this does not undergo prompt expansion.
The forms with `<' truncate at the left of the string, and the
forms with `>' truncate at the right of the string. For
example, if the current directory is `/home/pike', the prompt
`%8<..<%/' will expand to `..e/pike'. In this string, the
terminating character (`<', `>' or `]'), or in fact any
character, may be quoted by a preceding `\'; note when using
print-P, however, that this must be doubled as the string is
also subject to standard print processing, in addition to any
backslashes removed by a double quoted string: the worst case
is therefore `print-P"%<\\\\<<..."'.
If the string is longer than the specified truncation length, it
will appear in full, completely replacing the truncated string.
The part of the prompt string to be truncated runs to the end of
the string, or to the end of the next enclosing group of the
`%(' construct, or to the next truncation encountered at the
same grouping level (i.e. truncations inside a `%(' are
separate), which ever comes first. In particular, a truncation
with argument zero (e.g. `%<<') marks the end of the range of
the string to be truncated while turning off truncation from
there on. For example, the prompt '%10<...<%~%<<%# ' will print
a truncated representation of the current directory, followed by
a `%' or `#', followed by a space. Without the `%<<', those two
characters would be included in the string to be truncated.